Copper phthalocyanine pigments are a series of excellent pigments, and feature having a colorful blue shade and various superb fastness or resistance properties. In particular, C.I. Pigment Blue 15:3 (hereinafter abbreviated as “PB15:3”) and dispersion-stabilized C.I. Pigment Blue 15:4 (hereinafter abbreviated as “PB15:4”), which are both in the form of β crystals, are each abundantly used as cyan color, one of the three primary colors employed in process printing, over years. In recent years, however, the use of pigments as colorants is spreading in a variety of new image recording methods, led by the electrophotographic recording method, inkjet recording method and thermal transfer recording method, in addition to the conventional printing method using a machine plate. In such applications, requirements different from those required conventionally have arisen for cyan color. Described specifically, these recording methods have imposed, for the realization of still better color reproducibility upon formation of images, new keen requirements for a pigment, which has a bluish green color as a substitute cyan color for conventional copper phthalocyanines of blue color, and also for a colorant making use of the pigment and enabling high-chroma, colorful image recording (which may hereinafter be called an “image recording material”).
The above-described conventional copper phthalocyanine pigments (PB15:3 and PB15:4) are excellent in dispersibility, density, light fastness, heat resistance, electrostatic chargeability and safety. Nonetheless, they are too reddish than a desired cyan color when used singly, and may hence be used in combination with C.I. Pigment Green 7, C.I. Pigment Green 36, C.I. Pigment Green 58 or the like to correct their colors. In such a case, however, colors of considerably different hues are subjected to subtractive color mixing so that the resulting image tends to be provided with reduced chroma. Moreover, there is also a problem of load on the environment upon disposal because the above-described pigments to be used in combination contain halogen atoms in their structures.
Known cyan pigments other than the above-described, conventional copper phthalocyanine pigments include those to be described hereinafter. Phthalimidomethyl derivatives and the like of copper phthalocyanine are described in Patent Document 1. However, no description is made about their synthesis processes in Patent Document 1. When the present inventors synthesized these pigments in a manner known per se in the art, no tinting power inherent to the pigments was obtained due to the inclusion of impurities in large amounts, and the pigments were low in chroma. It was, therefore, impossible to obtain colorful images. Patent Document 2 describes a formula representing a phthalimidomethyl derivative, which may contain desired substituent group(s), as a copper phthalocyanine derivative having a substituent group on one or more benzene rings. However, the derivative called “PIM”, which is described in one of the comparative examples, contains no substituent group other than a phthalimidomethyl group on the phthalocyanine structure, and there is no example in which any other substituent group or groups are used. Obviously, no description is made about the color features of such derivatives. Mixtures of copper phthalocyanine and nickel phthalocyanine as described in Patent Documents 3 and 4 are not practically usable in applications such as toners for electrophotographic recording and inks for inkjet recording, because nickel phthalocyanine is a material having a problem in safety.
Patent Document 5 describes a copper phthalocyanine having phthalimidomethyl group(s), and specifies that the number of the phthalimidomethyl group(s) is 0.6 to 2.1, the number of sulfonic group(s) is 0.2 to 2.5, and as an additional essential requirement, the sum of these numbers is not greater than 3. However, the above material described in Patent Document 5 is intended as a crystal growth inhibitor or dispersion stabilizer for pigments, and Patent Document 5 contains no disclosure about a pigment exhibiting a bluish blue hue of high chroma such as that intended in the present invention.
Patent Document 6 discloses a process that reacts paraformaldehyde and phthalimide or a substituted phthalimide with copper phthalocyanine, a process that reacts copper phthalocyanine with bis-phthalimidomethyl ether or a substituted bis-phthalimidomethyl ether, and a process that reacts copper phthalocyanine with N-hydroxymethylphthalimide or a substituted N-hydroxymethylphthalimide, all, in an acidic solvent such as concentrated sulfuric acid. No description is, however, made about a sulfonated, phthalimido-containing phthalocyanine derivative in its examples.
Copper phthalocyanine pigments are extremely good in the shade, tinting power and various fastness or resistance properties of a colorful blue color compared with other blue pigments. Attempts have, however, been made in recent years to change copper, which is a heavy metal, to other metals or non-metals. In Patent Document 7 and the like, various pigments are proposed, including those which have been put into commercial products. Even with these non-copper, metal phthalocyanines pigments or non-metal phthalocyanine pigments, no bluish green pigments have, however, been realized to fully meet such a greenish blue hue of high chroma as mentioned above and long-awaited in the recent new recording methods.